Process for the production of carboxylic esters



The present invention relates to an improved process for the production of carboxylic acid esters by using, as the raw materials, the corresponding carboxylic acids or the anhydrides thereof and alcohols. More particularly, the invention relates to a process for producing the'esters of aliphatic, aromatic or heterocyclic carboxylic acids by the reaction of the carboxylic acids or the anhydrides j 20 thereof with alcohols in the presence of a catalyst such as,

an inorganic acid, an organic acid, or an ion-exchange resin with the addition of a peroxide.

Hitherto, as a process for the production of carboxylic acid esters, there have been known various processes. These processes, however, have in general required an excessive amount of alcohols to raw material carboxylic acids. Further, there is also known a process wherein in order to remove Water formed during the esterification another component that can form an azeotropic mixture with water is added to the reaction system and a process wherein a small amount of a material such as an inorganic acid having a catalytic action together with an action of dehydrating thus formed water is added to the reaction system. However, these processes are also insufficient in the points of the formation rate of the ester and of the yields, and therefore are unsatisfactory for industrial purposes.

The inventors have found that when a peroxide is added to a reaction system in a known esterification by heating a mixture of an aliphatic, aromatic, or heterocyclic carboxylic acid or the anhydride thereof and an alcohol under the presence of a catalyst, such as, an inorganic acid, organic acid or cation-exchange resin, the corresponding carboxylic ester acid can be produced in an extremely short time with a good yield as compared with known processes.

That is, in accordance with the process of this invention, 'by adding a peroxide to a reaction system in a known esterification process in which an aliphatic, aromatic, or heterocyclic carboxylic acid or the anhydride is caused to react with an alcohol under the presence of a catalyst selected from an inorganic acid, organic acid, or ionexchange resin by heating, the reaction time can be reduced from to A of that in the known processes and also the necessary amount of the alcohol to the carboxylic acid feed can be reduced from /2 to A of that in the known processes. By the process of this invention, the desired esters of aliphatic, aromatic, and heterocyclic carboxylic acids can be produced extremely easily and with a good yield.

As aliphatic carboxylic acid used in the process of this invention, there are formic acid, acetic acid, propionic acid, butyric acid, valerianic acid, caporic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and other aliphatic carboxylic acid that can be esterified. The aliphatic carboxylic acid may have a substituent such as an aromatic ring or a heterocyclic ring as the case may be. As the aromatic carboxylic acids, there are monocyclic and polycyclic aromatic carboxylic acids such as having a benzene ring, naphthalene ring, phenanthrene ring, etc, which may have a substituent as the case may be. For

3,322,772 Patented May 30, 1967 example, benzoic acid, phthalic acid or anhydride, toluic acid and salicylic acid may be mentioned. As the heterocyclic carboxylic acids, there are given the esterifiable carboxylic acids of monocyclic or polycyclic heterocyclic compounds of nitrogen, oxygen, sulfur, etc., which may have a substituent as the case may be. 7

As the alcohols, there are primary alcohols, such as, methyl alcohol, ethyl alcohol, and butyl alcohol; secondary alcohols, such as, isopropyl alcohol and isoamyl alcohol; tertiary alcohols, such as, t-butyl alcohol and tamyl alcohol; polyhydric alcohols, such as ethylene glycol and glycerol; and aromatic, and heterocyclic alcohols, such as, phenols, benzyl alcohol, phenylethyl alcohol, furs furyl alcohol and tetra-hydrof-urfuryl alcohol. These alcohols may have other substituents further.

As the catalyst, known esterification catalysts can be used, for example, an inorganic acid, such as, hydrochloric acid and sulfuric acid; an organic acid, such as, an organosulfonic acid, 'e.g., benzenesulfonic acid and p -toluenesulfonic acid, etc., and an organo-phosphoric acid; and cationic ion-exchange resin.

In carrying out the process according to the presen invention an inorganic peroxide, such as, hydrogen peroxide, perborate, persulfuric acid, peroxymonosulfuric acid, ammonium persulfate, metal peroxides e.g., barium peroxide, sodium peroxide, etc., and an organic peroxide such as acetylperoxide, benzoyl peroxide, perbenzoic acid, etc., can be used. Further, all compounds that can form these peroxides in the reaction system can be also used.

In the process of this invention, the using ratio of the carboxylic acid to the alcohol as the raw material is preferably a stoichiometric ratio, but on considering the cost of each raw material, the ratio may be suitably changed.

By a preferred embodiment of this invention, if the inorganic acid catalyst is used, for example 0.2-0.5 mole of concentrated sulfuric acid to 1 mole of the carboxylic acid or the anhydride is added into the raw material, and if the organic acid catalyst is used, for example 0.01- 0.02 mole of p-toluenesulfonic acid is added into the raw material together with for example about 0.2-1.5 mole, preferably 0.3-0.5 mole of 30% hydrogen peroxide as the peroxide in each case. By heating with refluxing the mixture, the esterification is finished in a short time.

By treating thus obtained reaction product by a conventional process, a desired carboxylic acid ester can be obtained with a yield of 100%.

The following examples are given to explain the process of this invention more in detail, but it should be understood that the invention is not limited to these examples.

Example 1 In the example, ethyl acetate was prepared;

Example 2 Ethyl acetate was prepared as;

benzoyl peroxide In a reaction flask equipped with a reflux condenser were placed 60 g. of glacial acetic acid, 92 g. of ethyl CIISCOOH C2H50}I CHsCO.OC2H5 3 alcohol, 49 g. of concentrated sulfuric acid, and 2.4 g. of benzoyl peroxides. They were heated for 15 minutes in an oil bath at 130 C. and treated by a conventional method. By the treatment, 81.5 g. of the ester having a Example 24 Dimethyl phthalate was prepared as;

boiling point of 7578 C. was obtained with a yield of 5 92.6%. H2804 -c00cI-n Similarly, the following esters were obtained from the O 2CH OH 2 2 11,0 corresponding raw materials by using the same inorganic "Coocm acid catalyst and various peroxides. 00

Example Compound B P orM.P. Reaction Yield .lmm. Peroxide used time (min) (Percent) 3 Methyl formate 7 96.6 4 Ethyl f0rmate 5 95.9 5 Ethyl propi0nate 5 78.6 6 do 5 75. 0 7 Ethyl valerate G 88.5 8 Methyl caprylate- 6 86 9 Methyl capzate... 9 83.3 10 Methyl laurate- 12 97. 6 11 Methyl myristate. 8 97.1 12 Methyl palmitate (M.P. H O; 10 96. 3

141-142 Peracetic acid 10 100 110-111 2 2 12 100 157 Sodium perborate. 10 91 Example 16 Ethylene glycol dipropionate was prepared as;

In a reaction flask having a reflux condenser were placed 1 mole of phthalic anhydride, 2.5 moles of methyl alcohol, 1 mole of concentrated sulfuric acid, and 0.3 mole of hydrogen peroxide and they were heated for 20 minutes in an oil bath at -95 C. When the content was homogenized, the reaction reached the end. After the reaction, by treating the reaction product with a conventional method, 184 g. of dimethyl phthalate having a boiling point of 138140 C./8mm. Hg was obtained with a yield of Similarly, the following esters were obtained from the corresponding compositions.

Ex. Compound 13.1. or Ml. Time Yield C./mm. Hg) (min) (percent) Dibutyl phthalatc 340 23 J2 Methyl benzoate 98/30 20 I 100 Methyl salicylate -121/30 25 96 Phenyl salicylate. (ll'LP: 41-42) 20 88 Methyl p-nitrobenzoate (M.P. 98) 18 97. 8 Methyl cinnamate (M.P. 34. 5) 15 9G. 9 Isoamyl cinnamate. 148-152/35 20 90. 8 Benzyl cinnamate (M.P. 38-39) 98. 5 Tetrahydrolurluryl benzoate 139-140/2 20 89. 5

1 Catalyst: perberlzoic acid.

Exam le 34 V drogen peroxide, and they were heated 111 an oil bath for 55 p about 15 minutes at 140-150 C. By treating the re- Methyl benzoate was prepared as; action product by a conventional method, 15.5 g. of the COOH COOCH3 ester having a boiling point of 211-213 C. was obtained. 7 The yield was 89%. Organic acid Similarly, the following esters were obtained from the 60 01.13011 cor-responding raw material compositions by using hy- H201 drogen peroxide as the peroxide.

B.P. C./ Reaction Yield Ex. Compound mm. Hg) time (Percent) (min.)

Benzyl acetate 213-214 10 93 Ethylene glycol. diacetate 189-191 18 89 Glycerol triacetate /40 120 96. 5 Benzyl butyrate 238-239 12 87.6 Phenylethyl formate 102-105/14 20 91 Phenylethyl propionate 210-212 15 86.9 23 Furluryl acetate 176 8 98.1

In a reaction flask equipped with a reflux condenser were placed 12.2 g. of benzoic acid, g. of methyl alco'hol, 0.2 g. of p-toluenesulfonic acid, and 6 ml. of hydrogen peroxide and they were heated for about 18 6 What is claimed is: 1. In the process for the production of a carboxylic acid ester by the esterification of a carboxylic acid selected from the group consisting of aliphatic carboxylic acids,

minutes in an oil bath at 130140 C. By treating the re 5 aromatic carboxylic acids, and heterocyclic carboxylic action product by a conventional method, 13 g. of the acids with an alcohol by heating the said carboxylic acid ester having a boiling point of 98-99" C./ 3 0mm. Hg was in the presence of a catalytic amount of a catalyst selected obtained. The yield was 95.6%. from the group consisting of inorganic acid catalyst, organic acid catalyst and cation-exchange resin catalyst,

Example 10 the improvement of adding peroxide to the reaction systern in a mole ratio of peroxide to carboxylic acid of from Methyl 1S0 nlcotmate was prepared as, 0.01 to 0'5: 1.

COOH 000cm 2. The process as claimed in claim 1 wherein the peroxide is an inorganic peroxide. H2804 1 3. The process as claimed in claim 2 wherein the in- OmOH W H2O organic peroxide is hydrogen peroxide. 4. The process as claimed in claim 2 wherein the inorganic peroxide is a perborate.

In a reaction flask equipped with a reflux condenser 5. The process as claimed in claim 2 wherein the inwere placed 6.2 g. of isonicotinic acid, 4.8 g. of methyl 0 organic peroxide is a member of the group of alkali metal alcohol, 9.8 g. of concentrated sulfuric acid and 3 ml. of and alkaline earth metal peroxides.

30% hydrogen peroxide. They were heated for about 20 6. The process as claimed in claim 2 wherein the inminutes in an oil bath at 140 C. and treated by a convenorganic peroxide is ammonium persulfate.

tional method to give 6.4 g. of the ester having a boiling 7. The process as claimed in claim 2 wherein the inpoint of 102103 C./ 20 mm. Hg. The yield was 94%. 25 organic peroxide is apersulfuric acid.

Similarly, the following esters were produced from the 8. The process as claimed in claim 1 wherein the corresponding raw material compositions. peroxide i an organic peroxide.

Ex. Compound B.P. or M.P. Time Yield CJmJn. Hg) (min) (percent) Ethyl furan-2-earboxylate (MP. 35. 5-36) 16 100 Methyl 2-pheny1quinolin-4-carboxyl- (M.P. 51-52) 15 91. 5 ls dyl iuran-Zcarboxylate 80-83/6 15 82.5 Benzyl furan-2-carboxylate 107-110/9 5 100 t-Butyl thiopheneZ-earboxylate 63-65/16 8 91 (2Oxyethyl) thiophene-Z-carboxylata. 80-84/8 8 94 Example 42 Ethylene glycol dipropionate was prepared as;

CH20H 2021150 0 o H CHzOH cationic ion-exchange resin OHgO.OO.OzH

corresponding compositions.

Example 43:

Compound Glycerol triacetate B.P. C./m-m. Hg) 170/40 Time (min) 70 Yield (percent) 80 9. The process as claimed in claim 8 wherein the organic peroxide is benz-oylperoxide.

10. The process as claimed in claim 8 wherein the organic peroxide is acetylperoxide.

11. The process as claimed in claim 8 wherein the organic peroxide is perbenzoic acid.

References Cited UNITED STATES PATENTS 1/ 1959 Skinner 23207 6/1965 Spoors et al 260-453 FOREIGN PATENTS 739,609 11/ 1955 Great Britain.

OTHER REFERENCES Subrahamanyam et al.: I. Am. Oil Chemists Soc., vol. 41, pp. 275-9, abstracted in Chem. Absts., vol. 61, col. 848-9.

ALEX MAZEL, Primary Examiner.

DONALD G. DAUS, Assistant Examiner. 

1. IN THE PROCESS FOR THE PRODUCTION OF A CARBOXYLIC ACID ESTER BY THE ESTERIFICATION OF A CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC CARBOXYLIC ACIDS, AROMATIC CARBOXYLIC ACIDS, AND HETEROCYCLIC CARBOXYLIC ACID WITH AN ALCOHOL BY HEATING THE SAID CARBOXYLIC ACID IN THE PRESENCE OF A CATALYTIC AMOUNT OF A CATALYST SELECTED FROM THE GROUP CONSISTING OF INORGANIC ACID CATALYST, ORGANIC ACID CATALYST AND CATION-EXCHANGE RESIN CATALYST, THE IMPROVEMENT OF ADDING PEROXIDE TO THE REACTION SYSTEM IN A MOLE RATIO OF PEROXIDE TO CARBOXYLIC ACID OF FROM 0.01 TO 0.5:1. 